Background Information. Radio Frequency Identification Systems (RFIDs) are used in a variety of industries to provide various types of information. This information may include information regarding the identity of the package, the location of the package, special handling instructions related to the package or its delivery, or a variety of other types of information related to these devices. A typical RFID system typically includes at least one active transmitting and receiving device commonly called a Reader/Writer or Interrogator and at least one passive or active target device, typically called a tag. The basic principal of such a system involves the transmission of radio frequency energy from the Reader/Writer to the tag. The tag receives the signal, modifies that energy and reflects this modified signal back to the reader, where this return signal is received, read and decoded.
RFID systems can be used in a variety of applications. One of the most common types of applications involves an embodiment where RFID tags are placed upon something that moves and a Reader is used by another party to interrogate a group of items such as packages to find a particular package which contains a particular tag.
The transmission of information and power between the reader and the tag is typically accomplished by the modulation of the RF carrier. Information is many times transferred using a backscatter technique. In this backscatter technique, radio frequency (RF) energy incident on the tag antennae is modulated by changing the impedance of the antenna and effectively changing the radar cross section (RCS) of the tag and the amplitude of the energy reflected back to the reader.
In other instances, the tag impedance is such that the tag absorbs the RF energy, which is then used to power the tag. The tag changes the antenna impedance following the timing requirements of the specific tag classification effectively increasing the reflectivity of the tag and amplitude of the backscattered carrier received at the Reader. In these systems, the reader provides power to passive tags by maintaining a constant RF carrier throughout the entire transaction with the tag.
In some circumstances, this constant sending of a signal combined with the backscattered response signals can be problematic particularly in applications where the reader is in close proximity to a plurality of tags or when the reader and the tags are in close contact with one another. This close association of the tags can cause the compression of signals as well as the compression of the modulated signals emanating from these tags. This results in signals that are difficult to separate or individually ascertain. This is particularly true of environments where the reader is also attempting to write information to this tag.
A variety of attempts to modify this information have been made with various levels of success, however providing a lost cost effective solution to the aforementioned problems has stood as a barrier to the wide spread use of such devices in various industries and channels of commerce.
What is needed therefore is a device that allows labels with RIFD tags to be dispensed and programmed from a single location. In order for this need to be met a RFID reader writer must exist that has sufficiently short range so as to program a single tag without affecting a plurality of tags that are located in another location. In addition, this device must be made of sufficiently low cost parts so as to make such a device commercially feasible.